Conventional electrical blankets comprise a woven fabric having the warp and filling ends so interlaced that at desired intervals channels are formed through which the wires of the heating element are drawn. The fabric is produced from spun fibers which are napped so that the blanket's finish appears quite similar to a nonelectric blanket. In use, the nap entraps air warmed by current flow through the wires so as to distribute heat throughout the blanket.
A deficiency of electric blankets of the type just described is that the nap tends to "pill" and become nonuniform as the blanket is subjected to use. This is detrimental not only to the blanket's appearance, but also with respect to its ability to evenly maintain the heat generated by the electrical elements. As a result, "hot spots" develop in the blanket.
In U.S. Pat. No. 3,528,874 which issued on Sept. 15, 1970, there is disclosed a blanket construction completely different from a conventional napped blanket. More particularly, an open mesh scrim substrate is interposed between layers of foam. The exposed surfaces of the foam are flocked to give a luxurious appearance and feel to the construction. The resultant product also is lightweight, supple and durable.
Inasmuch as the foam layers in a flocked blanket include permanent air cells, such a construction appeared attractive for modification to an electric blanket since air entrapped in the foam cells could be heated to uniformly distribute the heat throughout the blanket without concern that deterioration would produce "hot spots". Accordingly, efforts were undertaken to produce such a blanket.
In accordance with U.S. Pat. No. 3,528,874, the foam surfaces which face the scrim are flame-laminated together. This is possible because the scrim interposed between the foam layers is a very open mesh. Obviously, however, such a flame-lamination process does not lend itself to the formation of the channels required to receive electrical heating wires.
In order to overcome this problem, a flocked electric blanket was constructed by adhesively bonding first and second layers of polyurethane foam to respective sheets of nylon tricot fabric. The exposed surface of one of the nylon tricot sheets then was subjected to the selective application of adhesive so that when the two tricot sheets were brought together, channels were formed in accordance with the adhesive pattern. Thereafter, the exposed surfaces of the foam were flocked and the heating wires were inserted within the channels to complete the blanket construction.
The technique for producing a flocked electric blanket just described suffered several deficiencies. An important shortcoming was the expense of production resulting from the several adhesion steps of the process which required considerable time to accomplish. Furthermore, because of the use of the tricot sheets, the resultant blanket was quite stiff and considerably heavier than conventional flocked blankets.
The deficiencies just described cannot be overcome by using in place of tricot the woven fabric employed in conventional napped electric blankets. This is because a fabric suitable for napping must be formed from spun fibers, and to provide strength to such a fabric, coarse yarns must be included. In a flocked blanket, the use of a nappable fabric as a substrate would impart stiffness, weight and expense to the product. Also, its coarse yarns would produce a corduroy-like appearance in the finished blanket.